Beginner problems using DAC7714

[tardishead]

I am fairly new to Arduino. I have used some basic DACs like MCP4822 and 4922 but I need some help getting a DAC7714 up and running.
I have 7714 outputting different voltages but they have lots of errors. I have already verified my code on a Blackpill STM32 and a MCP4922 DAC so I conclude that the errors are from the SPI data stream
I am using SPI MODE3 which I believe to be correct
First of all I don't know what SPI speed is needed. The MCP4822 datasheet specs 20mhz but there is no data/suggestion for the DAC7714.
Data says CS and CLK are interchangeable and OR'd together. I am only using one chip so I presume I should either hold CS LOW or tie it to GND. This way I can also avoid the condition of shifting bits if CS rises before CLK has risen.
The timing diagram I am really struggling with. It also specifies a minimum time for LOADDACS to be held LOW after the clocks final rise (45ns). Is this what determines the clock speed. 45ns for half a clock cycle would mean 90ns for a whole cycle and lead to a clock speed of maximum 11.11MHZ

SPI.beginTransaction(SPISettings( 40000000, MSBFIRST , SPI_MODE3)) ;
digitalWrite (loadDacPin , HIGH) ;
SPI.transfer16(dac_one | buff[0][playCursor] ) ;
digitalWrite (loadDacPin , LOW) ;
SPI.endTransaction () ;

[pylon]

@tardishead

First of all I don’t know what SPI speed is needed. The MCP4822 datasheet specs 20mhz but there is no data/suggestion for the DAC7714.

Add the minimal clock times (would be 80ns but as most microcontrollers have symmetric low/high times, you get 100ns which is 10MHz). Keep in mind this is the maximum value you should stay below that in an actual setup, so I recommend 4 MHz or 8MHz if you need the speed and have very short SPI traces.

@tardishead

Data says CS and CLK are interchangeable and OR’d together. I am only using one chip so I presume I should either hold CS LOW or tie it to GND.

Although you could theoretically do that I recommend against it. Use it as you would do with any SPI device.

As CS doesn't start a new communication you should connect the RESET signal to put the chip in a known state at startup of your code.

You might use an inverter to provide the LOADDACS signal from the CS to save one pin on the controller.

@tardishead

The timing diagram I am really struggling with. It also specifies a minimum time for LOADDACS to be held LOW after the clocks final rise (45ns). Is this what determines the clock speed. 45ns for half a clock cycle would mean 90ns for a whole cycle and lead to a clock speed of maximum 11.11MHZ

No, you can leave LOADDACS low for a long time it just have to be low for at least 45ns. Given the maximum SPI clock frequency of 10MHz (see above), this shouldn't be a problem if you switch that signal at the same time as CS.

[tardishead]

Thanks for your help and explanation